Hello and Welcome! I'm Billy and i will assist you with your inquiry. Feel free to ask if any further info is needed.
This means that you either really have a low oil pressure, or a problem with the electronics (engine computer, intrument cluster, or wiring).
The most likely would be a low oil pressure. Having already replaced oil, filter and switch, next you need to look at the strainer, so the oil sump needs removing. at what intervals did you usually replace engine oil?
which oil do you usually use?
when at low revs, and you have the warnings, how does the engine sound (normal, louder, ticking noises etc...)?
and do you have any other engine problems or noises?
at the time this happened the fuel filter and fuel pipe harness were replaced, due to the primer bulb failing
also the engine sounds normal when ticking over
the oil normally used is 5w40 Fully Synthetic
don't know if its related (but there is an electronic fault) the outside air temperature doesn't display correctly its stuck at -2C the probe in the door mirror was replaced with a used probe but the issue remains
the problem wasn't there before the mechanic changed the filter and fuel pipe harness it was a problem when i got the car back, don't want to use that mechanic again
engine oil usually changed at 12,000miles
Using the right oil, and having the problem start right after replacing the harness, i would first check the wiring.
Check the wiring from the oil pressure switch, getting to the bulkhead to enter the cluster.
If the wiring is good (continuous, with clean and tight contacts), and having checked the engine ground cable (thick cable from chassis to engine, and if the problem persists, then you would need to have the oil pressure checked.
On your model you should get around 3.5 bars at 4000 rpm. This would confirm that the oil pump (pressure in general) is up to norm.
On you r model, the pressure should be 3.5 bars at 4000 rpm. This would confirm that the oil pump (pressure in general) is up to norm, and the problem is electrical.
If you have low pressure, then it would be either the strainer (clogged), or the pump requiring replacement.
Get back to me with your results, or if further info is needed. Thank you in advance for the positive rating!